1. Field
The invention relates to an active device having variable energy/light transmission properties comprising an active system between a protective substrate and a protective cover.
2. Description of the Related Art
The first types of active system related to the invention are essentially inorganic electrochemical systems, in particular essentially inorganic (mineral) electrochromic glazings, which are used to adjust the light and heat transmission, described for example, in particular, in patents EP-867 752, EP-831 360, PCT/FR00/00675, PCT/FR99/01653, the electrolyte being in the form of an essentially mineral layer, all the layers of the system then being essentially mineral. This type of electrochromic system is commonly designated by the term “all-solid” electrochrome. In general, these essentially inorganic electrochromic systems comprise two layers of electrochromic material separated by an electrolyte layer and framed by two electroconductive layers forming electrodes.
Systems called “light valves” also exist: these are polymer based films in which microdroplets are placed containing particles capable of moving into a preferential direction under the action of an electrical field. An example thereof is described in patent WO93/09460.
Liquid crystal systems also exist, having an operating mode similar to the preceding ones: they use a polymer film placed between two conductive layers and in which liquid crystal droplets are dispersed, in particular nematic having a positive dielectric anisotropy. When the film is energized, the liquid crystals are oriented in a preferential axis, thereby allowing viewing. When deenergized, the film becomes hazy. Examples thereof are described in patents EP-238 164, U.S. Pat. Nos. 4,435,047, 4,806,922, 4,732,456. Mention can also be made of cholesteric liquid crystal polymers, like those described in patent WO92/19695.
A second type of active system to which the invention is related concerns the layers or stacks of layers of which the properties are changed without electric power supply, under the effect of heat or light: mention can be made of thermochromic layers, in particular based on vanadium oxide, thermotropic layers or mineral or organic photochromic layers, in particular polymers, which may be in the form of polymer films or even gel films. This is in particular the case of thermotropic gels, for example those described in patents EP 639 450, U.S. Pat. No. 5,615,040, WO 94/20294 and EP 878 296.
A fourth type of active system concerns a gasochromic system of which the properties are modified by the passage of a gas in particular comprising hydrogen, and made from a thin layer of WO3 often surmounted by a layer of platinum deposited on the surface of a glass element.
All these abovementioned systems have in common the fact that they may, to a more or less broad extent, be sensitive to mechanical, chemical aggression, or to contact with water, or to exchanges with the exterior.
These are the reasons why, to preserve their satisfactory operation, these active systems are commonly placed against at least one protective supporting substrate. They are usually placed between a protective substrate and a protective cover, for example made from glass, joined together by means of assembly polymer sheet(s) of the thermoplastic type.
Plastic leakproofing means are often provided, for the purpose of isolating the active system from the exterior to the maximum.
Leakproofing means are thus described in French patent 2 815 374, which relates to a laminated glazing with a system of plastic seals composed of a plurality of elements in order to simultaneously perform all the functions of isolation from gases, liquids, dust. Thus, a polyisobutylene based seal (barrier to gases) called butyl seal, is placed between the substrate and the cover, and a polysulfide or polyurethane seal (barrier to liquids), joined to the butyl seal.
However, these seals have several drawbacks. In fact, these seals must at best meet at least three requirements which are not necessarily compatible:                as we have seen, they must isolate the active system from the exterior. They must therefore play a barrier role as effectively as possible, even in the long term, in particular against water or any other solvent, and in its vapor form and/or in its liquid form, they must be capable of withstanding extreme climatic conditions, in particular a high moisture content and/or high temperature,        their utilization, the way in which they are installed, is not necessarily the simplest from the industrial standpoint,        and finally, their mechanical properties may be far inferior to those that may be required.        
It is the object of the invention to remedy these drawbacks, in particular by finding means for controlling the durability of such abovementioned devices with active systems, in order to improve and/or better control their reproducibility, particularly by means not putting into question the present manufacturing methods of these glazing type devices, and preferably which may tend to simplify them.